The purpose of these studies will be to look at the effect of positive end-expiratory pressure (PEEP) as a treatment modality on the lung injured by high concentrations of oxygen and compared with the effect on lung injury produced by intravenous injections of 0.05 ml/kg oleic acid. Initially, adult mongrel dogs will be used and following the experiments described in the next section, baboons will be used in this project. The basis for undertaking these studies revolves around the acquisition of a new Baird Atomic Scanning Camera Model No. 70 for study of ventilation and perfusion abnormalities in the animals. Initially, these studies will be done on normal dogs, then on a group of dogs exposed to high concentrations of oxygen and on a second group injected with IV oleic acid. These dogs will be ventilated with an MA-1 respirator and pulmonary artery, systemic, and left atrial pressure measured along with arterial blood gases. Wasted ventilation (VD/VT) will be calculated using the Bohr equation. V/Q ratios for the upper (region 1), middle (region 2), and lower (region 3) lung fields will be determine using the scanner and Xenon 133. Changes in V/Q at graded levels of PEEP at 5, 10, 15, and 20 cm H2O will be analyzed in each group.